SHOALING AND SCHOOLING BEHAVIOR

An Investigation of the Impacts of Current on Shoaling and schooling Behavior in Anchoa mitchilli and Fundulus heteroclitus

Shoaling and schooling Behavior in Anchoa mitchilli and Fundulus heteroclitus

Introduction

Shoaling is a social behavior seen in a variety of fish for multiple purposes. This behavior may aid in reproduction and the effectiveness of foraging, and help to reduce their susceptibility to predation (Blakeslee et al. 2009). Shoaling typically occurs with fish of comparable size, shape, and coloring (Blakeslee et al. 2009).

Fundulus heteroclitus has been found to show shoaling, schooling, and solitary characteristics (Frommen et al. 2009). Anchoa mitchilli is a high prey species and uses shoaling behavior for protection against predation. Investigating other factors that may influence shoaling patterns will aid in understanding stresses placed on different species, and show how their vulnerabilities to reproduction and predations are impacted.

The observation of racial differences within species, each race with divergent migration behaviors, may have been first recorded in the early nineteenth century when a Korean naturalist, Yak-Jun Jung, observed that herring (Clupea pallasi) found in the Yellow Sea contained fewer vertebrae than those from the Japan/East Sea (Jung, 1816). Early recognition of migratory races in the west rests firmly with Heincke ( Heincke, 1898; Sinclair and Solemdal, 1988), who observed that individuals collected from different spawning shoals of North Sea Atlantic herring (Clupea harengus) exhibited subtle but demonstrable morphometric differences. By sampling spawning shoals, Heincke recognized that common lineage preserved divergent migratory behaviors between races (populations).

Early emphasis on stocks focused on schools, or shoals, of fish. Indeed, Hjort's year-class paradigm (Hjort and Lea, 1914) was not immediately accepted due in part to its implication that population-wide phenomena (year-class dominance) would overshadow processes which controlled fish school abundance and membership. Hjort's most ardent critic, Thompson (1914) argued that Hjort and Lea's strong 1904 year-class of Atlantic herring was an artifact of combining individuals among schools. Hjort's theory of population regulation has played an important role in the conception of fish stock. If schools or shoals were commonly affected by pulsed recruitment events, then would it not be more beneficial for managers to consider aggregates based upon common spawning rather than those based upon common migration behaviors.

Increased perspective on the prevalence and ecological significance of divergent migrations has arisen through advancing technologies. Of these, otolith elemental analysis has seen especially rapid development and application over the past five years. In this paper, I preview insights, which might be on the horizon by addressing how divergent migrations can be incorporated into the stock concept. What does the emerging method of otolith composition tell us about fish stocks? Based upon otolith elemental fingerprinting, I evaluate Clark's contingent hypothesis for Hudson River striped bass and summarize examples of contingent behaviors for other taxa. An intriguing question is that if contingents exist, how are they regulated? Using frameworks for understanding ontogenetic niche shifts and density dependent habitat selection, I hypothesize that early life decisions regarding energy allocation (Metcalfe and Thorpe, 1992; Thorpe et ...